1. Field of the Invention
The device of the present invention relates to a new and improved safety switch for a lift system that is employed for lifting wheel chairs or the like from ground level to floor level of a transit vehicle.
2. Description of the Prior Art
Many present day transit vehicles include a lift assembly or lift system mounted within a doorway recess of the vehicle that includes a platform that in a first position defines one or more steps and in a second, extended position defines a platform that can be lowered from the floor level of the transit vehicle to the ground whereupon a wheel chair may be rolled onto the platform. Thereafter, the reverse action of the platform allows the wheel chair to be rolled onto the floor or the transit vehicle. A lift system of this type is disclosed in U.S. Pat. No. 4,180,366 and this patent is incorporated by reference herein.
Prior art lift assemblies of this type include sensitive edges at different locations on the platform such that upon engagement of the platform with the ground or a curb, a sensitive edge actuates a switch to terminate further downward movement of the platform thereby avoiding damage to the lift assembly. It has been discovered that sensitive edges on these platforms have deteriorated rapidly due to the effects of the environment and the repeated engagement with the abrasive surfaces such as concrete curbs, sidewalks and the like. As a result of this deterioration of the sensitive dyes the reliability of the standard switch to terminate operation of the lift assembly upon engagement of the curb or sidewalk is reduced. Consequently, if the sensitive edge has sufficiently deteriorated the lift assembly will continue to operate after engagement with an obstacle resulting in substantial torsional forces being applied to the lift assembly causing damage to the frame and other components and possibly to the transit vehicle.